diff -u -r boost/mp_math~/mp_int/ctors.hpp boost/mp_math/mp_int/ctors.hpp
--- boost/mp_math~/mp_int/ctors.hpp	2008-10-06 04:01:09.000000000 -0700
+++ boost/mp_math/mp_int/ctors.hpp	2009-01-09 16:31:29.000000000 -0800
@@ -260,6 +260,7 @@
 template<class A, class T>
 mp_int<A,T>::~mp_int()
 {
-  this->deallocate(digits_, capacity_);
+  if (digits_)
+    this->deallocate(digits_, capacity_);
 }
 
diff -u -r boost/mp_math~/mp_int/mp_int.hpp boost/mp_math/mp_int/mp_int.hpp
--- boost/mp_math~/mp_int/mp_int.hpp	2008-10-05 15:37:33.000000000 -0700
+++ boost/mp_math/mp_int/mp_int.hpp	2009-01-09 16:36:28.000000000 -0800
@@ -464,7 +464,8 @@
 {
   if (this != &rhs)
   {
-    this->deallocate(digits_, capacity_);
+    if (digits_)
+      this->deallocate(digits_, capacity_);
     digits_ = 0;
     used_ = 0;
     capacity_ = 0;
@@ -643,7 +644,8 @@
       n = new_cap;
     digit_type* d = this->allocate(n, digits_);
     std::memcpy(d, digits_, sizeof(digit_type) * used_);
-    this->deallocate(digits_, capacity_);
+    if (digits_)
+      this->deallocate(digits_, capacity_);
     digits_ = d;
     capacity_ = n;
   }